1. Field of the Invention
The present invention is related to integrated circuit (IC) and chip design systems and more particularly to computer aided design (CAD) systems for designing ICs and IC chips.
2. Background Description
Semiconductor technology and chip manufacturing advances have resulted in a steady decrease of chip feature size to increase on-chip circuit switching frequency (circuit performance) and the number of transistors (circuit density). Typical semiconductor integrated circuit (IC) chips are multilayered units with circuit layers stacked such that layer features overlay one another to form individual devices and connect devices together. Individual layers normally are patterned lithographically using well known photolithographic techniques as applied to semiconductor manufacturing. Normally, a chip designer creates an electrical or logic representation of a new chip that is converted to a chip/circuit layout. The chip/circuit layout is converted to mask shapes that are printed on photolithographic masks. Each photolithographic mask is used to print a pattern on a semiconductor wafer, which may define local wafer properties or one of the chip/circuit layers.
Previously, both design and manufacturing have operated on the assumption that the geometries of the designed layout and manufactured wafer, as well as those of the photomasks used to transfer the design geometries to the wafer, closely resemble each other. As semiconductor technology has pushed the limit of physical processes and materials, this assumption is no longer valid. As a result, increasing creativity, effort and expense has been necessary for design, lithographic patterning and manipulating the design data flow to manufacturing. In some cases, manufacturing costs and risks have made state of the art layout methodology and supporting computer-aided design tools inadequate for producing manufacturable designs, i.e., fabricated wafers that exactly satisfy the properties intended/assumed/modeled in the design.
Thus, there is a need for design tools that reduce the cost and risk of layout generation and layout checking, and that improves the efficiency of layout data preparation. In particular, there is a need for design tools that improve design manufacturability, i.e., providing designs for which the fabricated wafers will more exactly satisfy the properties intended/assumed/modeled in the design phase, at lower manufacturing cost and risk.